Before you begin

Docker installed and running on your local machine,
and a Docker Hub account configured (we’ll use it for a container registry).

Recreating the sample code

Create a new file named helloworld.go and paste the following code. This
code creates a basic web server which listens on port 8080:

packagemainimport("fmt""log""net/http""os")funchandler(whttp.ResponseWriter,r*http.Request){log.Print("Hello world received a request.")target:=os.Getenv("TARGET")iftarget==""{target="World"}fmt.Fprintf(w,"Hello %s!\n",target)}funcmain(){log.Print("Hello world sample started.")http.HandleFunc("/",handler)port:=os.Getenv("PORT")ifport==""{port="8080"}log.Fatal(http.ListenAndServe(fmt.Sprintf(":%s",port),nil))}

In your project directory, create a file named Dockerfile and copy the code
block below into it. For detailed instructions on dockerizing a Go app, see
Deploying Go servers with Docker.

# Use the offical Golang image to create a build artifact.# This is based on Debian and sets the GOPATH to /go.# https://hub.docker.com/_/golang FROM golang:1.12 as builder# Copy local code to the container image. WORKDIR /go/src/github.com/knative/docs/helloworld COPY . .# Build the command inside the container.# (You may fetch or manage dependencies here,# either manually or with a tool like "godep".) RUN CGO_ENABLED=0GOOS=linux go build -v -o helloworld# Use a Docker multi-stage build to create a lean production image.# https://docs.docker.com/develop/develop-images/multistage-build/#use-multi-stage-builds FROM alpine RUN apk add --no-cache ca-certificates# Copy the binary to the production image from the builder stage. COPY --from=builder /go/src/github.com/knative/docs/helloworld/helloworld /helloworld# Run the web service on container startup. CMD ["/helloworld"]

Create a new file, service.yaml and copy the following service definition
into the file. Make sure to replace {username} with your Docker Hub
username.

After the build has completed and the container is pushed to docker hub, you
can deploy the app into your cluster. Ensure that the container image value
in service.yaml matches the container you built in the previous step. Apply
the configuration using kubectl:

kubectl apply --filename service.yaml

Now that your service is created, Knative will perform the following steps:

Automatically scale your pods up and down (including to zero active pods).

Run the following command to find the external IP address for your service.
The ingress IP for your cluster is returned. If you just created your
cluster, you might need to wait and rerun the command until your service gets
asssigned an external IP address.

# In Knative 0.2.x and prior versions, the `knative-ingressgateway` service was used instead of `istio-ingressgateway`.INGRESSGATEWAY=knative-ingressgateway
# The use of `knative-ingressgateway` is deprecated in Knative v0.3.x.# Use `istio-ingressgateway` instead, since `knative-ingressgateway`# will be removed in Knative v0.4.if kubectl get configmap config-istio -n knative-serving &> /dev/null;thenINGRESSGATEWAY=istio-ingressgateway
fi
kubectl get svc $INGRESSGATEWAY --namespace istio-system